A portable radio device with a collapsible structure ordinarily has a mechanism including an upper casing and a lower casing connected by a hinge so as to be freely open and close. Thus, the portable radio device can take an opening state and a closing state. The portable radio device has two advantages of a high visibility and an easy portability that a viewable display screen can be enlarged under a state that the device is opened and used (namely, an opening state) and the device can be made compact under a state that the device is closed and used (a closing state) from the viewpoint of such structural characteristics.
As an antenna of a foldable portable telephone, a protrusion type antenna disposed in a casing is disclosed in JP-A-2001-45123.
For such a protrusion type antenna, a helical antenna or an extensible mono-pole antenna is ordinarily employed. Since the antenna portion protrudes from the casing, an antenna gain can be raised while a hand holds the portable telephone.
However, since the antenna portion is protruded, when the portable telephone is taken out from a pocket or the like, the antenna may be sometimes caught by a part of the pocket so that the portable telephone is hardly taken out.
As compared therewith, as an antenna contained in the casing of the foldable portable telephone, a strip line antenna is disclosed in JP-A-10-308618. Further, in JP-A-2001-284934, a hinge portion contained antenna is disclosed. Further, in JP-A-2001-156898, an antenna contained in an upper casing is disclosed.
Still further, as a flip type antenna contained in the casing of the portable telephone, a coil type antenna is described in JP-A-9-64778 and a micro-strip line antenna is described in JP-A-10-190330.
Further, JP-A-10-84406 discloses a plurality of element contained antenna in which a dipole antenna as a radiation element contained in an upper casing is combined with a non-feeding element contained in a lower casing.
Since the above-described antenna contained in the casing has no part protruding from the casing, the antenna is not caught by a part of the pocket or the like. However, since the direction of a main polarized wave emitted from the antenna is limited to a specific direction, a difference is undesirably generated in the antenna gain between a case that the portable telephone is held by a left hand during speaking (a left hand speaking state) and a case that the portable telephone is held by a right hand (a right hand speaking state).
Further, in the hinge portion contained antenna, under a state in which the portable telephone is allowed to come near to the ear and the mouth to speak (refer this state as to a speaking state, hereinafter), when the hinge portion is held by a hand, the antenna gain may be sometimes undesirably deteriorated, because the antenna portion is covered with the hand.
Further, in the flip part contained antenna, while the flip part is closed, a portable telephone main body is allowed to come near to the antenna portion so that the antenna gain may be possibly deteriorated.
Still further, in the plurality of element contained antenna, while the upper and lower casings are opened to speak, when a part near the radiation element is covered with a hand, the antenna gain may be undesirably deteriorated.
It is an object of the present invention to provide a portable radio device having an antenna with a high performance under various using states.